A commercial nuclear reactor produces heat from which electricity is generated. The heat is produced by of fission of a nuclear fuel, referred to as a nuclide, such as enriched uranium. A control rod is used in a nuclear reactor to control the rate of fission of the nuclear fuel. Controlling a nuclear reaction is a matter of ensuring that the control rods are precisely positioned at the right time. The control rod is removed from or inserted into the central core of the nuclear reactor to control a neutron flux by increasing or decreasing the rate of fission of the nuclear fuel. Typically, one or more control rods are positioned vertically within the central core. A control rod drive mechanism (“CRDM”) is designed to insert, withdraw or maintain the position of the control rod. Typically, the CRDM is contained within a pressure housing that comprises a tubular extension of the reactor pressure vessel.
The CDRM typically is supported within the tubular pressure housing by a pair of angular contact ball bearings configured for use as a matched set. In general, each angular contact ball bearing includes an inner ring, an outer ring, and a plurality of rolling elements disposed between the inner ring and the outer ring. In many applications, the plurality of rolling elements is separated by a plurality of spacers wherein typically a spacer is positioned between a pair of rolling elements. Such a pair of angular contact ball bearings is commonly referred to as a “duplexed” pair of bearings and shall be referred to herein generally as a “duplex bearing.” The CDRM typically is supported by more than one pair of angular contact ball bearings, that is, more than one duplex bearing. The duplex bearings provide for precise location of a shaft positioned at least partially therein and are designed to meet operating parameters of a nuclear reactor.
Standard duplex bearings are fabricated by mounting or otherwise joining the pair of angular contact ball bearings to one another. There are three basic mounting methods to accommodate different loading requirements: Back-to-Back (referred to herein as a “B-Type” duplex bearing), Face-to-Face (referred to herein as an “F-Type” duplex bearing), and Tandem (referred to herein as a “T-Type” duplex bearing). Generally, B-Type and F-Type duplex bearings accommodate heavy radial loads, combined radial and thrust loads, reversing thrust loads and moment loads; while T-Type duplex bearings accommodate heavy radial loads and high one-direction thrust loads with minimum axial shaft deflection. Standard duplex bearings are fabricated such that there is a light axial pre-load induced on the bearing at nominal conditions. In some applications, increased bearing stiffness is provided by inducing a heavier axial load in the mounted bearing. Moreover, the axial load can be increased or decreased to meet the requirements of a particular application.
Typically, angular contact ball bearings include an outer ring having a generally cylindrical exterior surface and a generally cylindrical interior surface, and an inner ring having a generally cylindrical exterior surface and a generally cylindrical interior surface. The inner ring is disposed within the outer ring. A plurality of rolling elements such as balls is disposed in a cavity between the inner ring exterior surface and the outer ring interior surface such that the inner ring is rotatable with respect to the outer ring. In some rolling bearings, the plurality of rolling elements is disposed in a circular frame or cage which holds the rolling elements in place in the rolling bearing.